In recent years, display devices have been extensively used which are thin, light, and low in electric power consumption, and are typified by liquid crystal display devices. Such display devices have been popularly provided in, for example, mobile phones, smart phones, and laptop personal computers. In addition, development and widespread use of electric paper which is a thinner display device are expected to be accelerated in the future. Under such circumstances, reducing electric power consumption in various kinds of display devices is a common object at present.
A method in which peripheral circuits such as a control circuit and a driving circuit of a display device are stopped (intermittently driven) is known as a first method for reducing electric power consumption.
For example, Patent Literature 1 discloses a method for driving a display device which achieves lower electric power consumption by providing a pause period that is longer than a scanning period in which a screen is scanned one time.
Furthermore, a method for controlling a luminance of a backlight (hereinafter abbreviated to “BL”) in accordance with a result of detection of an external light intensity (hereinafter abbreviated to “BL control”) is known as a second method for reducing electric power consumption.
Moreover, a method for achieving low electric power consumption while causing only a specific peripheral circuit to continue operating in a low electric power consumption mode is known as a third method for reducing electric power consumption.
For example, according to Patent Literature 2, a sleep clock whose frequency is lower than that of a normal operation clock and does not cause a flicker in a display is supplied to a driving circuit of a liquid crystal display device while operation of a CPU (central process unit) is stopped, so that the flicker in the display is prevented while lower electric power consumption is achieved.